The present invention relates to a high voltage transformer winding assembly. More particularly, the present invention relates to a tunable high voltage transformer winding assembly for shaping the transformer output voltage waveform preferably in order to improve the voltage regulation thereof.
The present invention is particularly useful in the high voltage flyback transformer of a television receiver and in similar environments which require the development of a high voltage from a pulse input with a relatively moderate load current. In color television receivers, the desire for brighter pictures has placed greater demands on the cathode ray tube high voltage power supply. Increased brightness may be achieved by using a higher cathode ray tube anode voltage providing regulation of this voltage is not sacrificed. The higher anode voltage is theoretically relatively easy to produce by increasing the turns ratio of the flyback transformer. However, increasing the number of turns creates problems such as core saturation and sometimes an undesirable shift in the range of tuning. The concomitant need for good regulation presents an even more difficult problem. In addition, if the high voltage winding assembly comprises only a single winding, corona discharge problems arise when the number of turns in such a single winding is increased.
The invention described and claimed in the Von Fange et al application, referred to above, provides a means of solving these problems. It was found, in accordance with that invention, that by turning the high voltage winding assembly to predetermined resonant frequencies and by controlling the relative amplitude of the resonant frequencies, it is possible to generate a substantially rectangular high voltage output pulse with greatly improved voltage regulation. As set forth in the Von Fange et al application, a high voltage winding assembly is provided having a plurality of windings interconnected by diodes.
The selected spacing between windings and the selected height and width of the windings enable tuning of the high voltage windings assembly by adjusting stray capacitance, capacitance to space and to ground, interwinding capacitance and leakage inductance. The control of such parameters occasions a tuning of the multiple resonances of the winding assembly. While various frequencies and the amplitudes thereof are affected, control of a predominant frequency and its amplitude is primarily realized.
The present invention provides additional tuning flexibility by dividing the winding assembly into subassemblies located on different legs of the transformer core and providing for additional control of the leakage inductance and inter-subassembly capacitance by selecting the distance between the sub-assemblies. This selecting of the distance between the subassemblies affords additional tuning control over the frequencies making up the output pulse. Primarily the frequency and amplitude of a second predominant frequency are controlled.
In addition to the reduction of corona discharge problems by having a plurality of winding pairs interconnected with diodes as shown in the Von Fange et al application, the present invention provides a structure for further reducing the likelihood of corona discharge by positioning the a-c null of each winding adjacent the core. In this manner, the higher a-c voltages are spaced farther from the core reduing the a-c potential gradients since the voltage to distance ratio is decreased. This is achieved in accordance with the present invention by placing an a-c null or minimal a-c voltage on the start turns or innermost turns of each of the windings.
There are teachings in the prior art for combining two windings to form a winding pair. For example, U.S. Pat. No. 1,340,027 -- Dunham discloses two layer type windings wound in opposite directions which are mounted on a common tubular support with their start windings connected together to provide terminal connections on the outer surface of the coil with the two coils producing magnetomotive forces in the same direction. U.S. Pat. No. 3,886,434 -- Schreiner discloses a high voltage horizontal flyback transformer assembly in which a pair of layer wound coils are mounted on opposed legs of a single window magnetic core. Schreiner discloses that his transformer winding assembly requires no critical tuning elements and behaves essentially as an untuned system. Neither of these prior art references teach a tuned high voltage winding assembly and particularly do not teach varying the spacing between windings on different legs of a magnetic core in order to adjust the leakage inductance and capacitance of the winding assembly.